9. Safety of Bacillus 1315
9.2. Risk assessment 1353
Assessment of Bacillus probiotics in aquatic animal diets or in their rearing water against the 1354
potential risks is a significant issue The Bacillus used as probiotics need to be recognized to 1355
strain level with any infection in humans and aquatic animals. Also, such probiotic must not 1356
carrier the transferable antibiotic resistance genes. Bacillus able to produce toxins or cause 1357
hypersensitivity reactions in the target host are not suitable for probiotics. Since 2007 the 1358
European Food Safety Authority (EFSA) has been using a concept [Qualified Presumption of 1359
46 Safety, QPS), European approach for the assessment of the safety of probiotics] as a generic 1360
risk assessment tool to assess the safety of a microorganism such as Bacillus (EFSA, 2007).
1361
Bacillus as spore-forming bacteria are becoming popular as the promising probiotics for use in 1362
aquatic animal feed or in their rearing water because of their tolerance to fluctuations in the 1363
water temperatures that make them easier to handle during manufacture, storage and 1364
transportation of feed. A number of 13 Bacillus species including B. subtilis, B.
1365
amyloliquefaciens, B. licheniformis, B. coagulans and B. megaterium have been recognized by 1366
EFSA (2013) to be used as probiotics for animal feed including fish and shellfish. The safety 1367
of these Bacillus species was detected based on the absence of enterotoxins and emetic toxins.
1368
However, it is important to note that some Bacillus bacteria such as B. anthracis, B. cereus, B.
1369
thuringiensis are serious pathogens in humans and animals (e.g. Damgaard et al., 1997;
1370
Hernandez et al., 1998; Little & Ivins, 1999; Kotiranta et al., 2000.; Raymond et al., 2010).
1371
Despite a good information available about the pathogenesis of B. anthracis and B. cereus, no 1372
evidence of pathogenic effects for other endospore-forming bacteria is available. The emetic 1373
toxin (cereulide), enterotoxins haemolysin, non-haemolytic enterotoxin and cytotoxin products 1374
by B. cereus are well known toxins that can affect humans (e.g. Granum & Lund, 1997; Schoeni 1375
& Lee Wong, 2005). In a study by From et al. (2005) from 333 strains of different Bacillus 1376
species, eight strains of B. subtilis, B. mojavensis, B. pumilus and B. fusiformis were able to 1377
produce emetic toxins and cytotoxins. Also, some disorders such as cattle mastitis (Parkinson 1378
et al., 1999) and cattle abortion (Agerholm et al., 1997) have been reported by B. cereus and B.
1379
licheniformis, but no data available regarding aquatic animals. There are also some antibiotic 1380
resistance reports in Bacillus subtilis showing this bacterium carriers conjugative transposons 1381
e.g. Tn5397, which is able to transfer resistance to tetracycline encoded by the tet(M) gene 1382
(Mullany et al., 1990; Roberts et al., 1999) and tet(L) gene (Phelan et al., 2011) as well as 1383
macrolide-lincosamide-streptogramin B resistance determinants on the plasmid (Monod et al., 1384
1986).
1385
10. Conclusions 1386
Several reports exist in finfish and shellfish regarding the presence of Bacillus in the GI tract.
1387
However, when investigating Bacillus in the GI tract, one major concern popped up; several 1388
studies have focus to characterize the GI lumen communities (the allochthonous microbiota) 1389
and the gut microbiota from faecal samples, while fewer studies have focus on bacteria that 1390
adhere to the mucosal surface (the autochthonous microbiota) which may be important in 1391
47 specialized physiological functions. We therefore recommend in future studies, more focus on 1392
the autochthonous gut microbiota.
1393
Most previous studies evaluating Bacillus in the GI tract of finfish and shellfish were based on 1394
culture-based approaches, but this approach may be question. Although there is a discussion 1395
among scientists about the value and need of using culture-based techniques vs. culture-1396
independent approaches, it is apparent that viable cells are valuable to culture collections, in 1397
vaccine production, as well as their use in probiotics and synbiotic studies. During the last 1398
decades, the denaturing gradient gel electrophoresis (DGGE) method has been commonly used, 1399
but the method only detect 1-2% of the microbial diversity. Therefore, we recommend; next-1400
generation sequencing when evaluating the gut microbiome, including the presence of Bacillus 1401
species in the GI tract of finfish and shellfish species.
1402
Use of Bacillus bacteria as probiotics in feed or as biodegrading bacteria in the ponds rearing 1403
water and soil is now a sustainable motion to reduce the environmental impact induced by 1404
aquaculture industry. There are at least ten species of Bacillus used as the main components of 1405
commercial probiotic (bioremediation) products for improvement of water quality of aquatic 1406
animals. Bioremediation by some Bacillus strains in finfish and shellfish pond waters have 1407
revealed not only an increase in the bioremediation efficacy, but also improved survival of the 1408
cultured animals. These probiotic Bacillus species are a well tool by maintaining a higher 1409
density of beneficial bacteria and a lower load of pathogenic agent in the ponds. As probiotics, 1410
Bacillus play a significant role in maintaining optimum water quality parameters particularly 1411
toxic gases including ammonia, nitrite, nitrate, hydrogen sulphide and carbon dioxide 1412
throughout the growing period with a significant reduction of stress level. Elimination of 1413
stressors, thus lead to an optimum immuno-physiological balance in the target animal with a 1414
better growth performance and survival rate as the final consequence of the aquaculture activity.
1415
Therefore, the application of Bacillus as probiotics in aquaculture is growing rapidly, 1416
particularly in the regions where intensive aquaculture systems have been developed. Bacillus 1417
probiotics as components of biocontrol products either in feed or in water column and sediment 1418
are often used as a mixture of different species to provide a range of beneficial effects on 1419
aquaculture systems. Bacillus as the ubiquitous bacteria in sediments are also naturally ingested 1420
by aquatic animals. Also, study about the effects of a particular Bacillus species or strains on 1421
different fish and shellfish species, age, growth condition, water quality condition and diet types 1422
48 can identify the condition in which the probiotics could work well. Bacillus spp. are not 1423
generally involved in horizontal gene transfer processes with Gram-negative bacteria e.g.
1424
Vibrio and Aeromonas. Thus, obtaining antibiotic resistance genes from these Bacillus 1425
probiotics is doubtful. Bacillus probiotics are able to rapidly replicate, tolerate a multitude of 1426
environmental conditions giving a wide range of beneficial effects in aquaculture sector. Also, 1427
the sporulation process by Bacillus probiotics enables them for the simple process and 1428
formulation as well shelf-stable probiotic spore products. However, some Bacillus species used 1429
as probiotics e.g. B. subtilis produce cytotoxic and emetic toxins. Therefore, detailed safety 1430
studies are recommended for these bacterial strains before to be used as the safe probiotics.
1431
Acknowledgements 1432
This research work was supported by University of Tehran and University of Morduch and 1433
their supports is fully acknowledged.
1434 1435
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